Method and systems for end of train force reporting

ABSTRACT

An EOT unit detects an excessive end of train force using an accelerometer and reports the excessive force. The report may be made to a device located off the train, to an event recorder in the EOT unit, and/or to another device located on the train such as a head of train unit and/or an event recorder located outside the EOT unit. The accelerometer may be a singe, dual, or tri-axial accelerometer. The message may be sent in response to the detection of the excessive acceleration or may be part of a periodically transmitted message from the EOT unit to a HOT unit. A HOT unit is configured to receive a message indicating an excessive EOT acceleration and display an indication of the excessive acceleration to the operator and/or record the message in an event recorder and/or report the excessive acceleration to a device located off the train.

FIELD

The invention relates generally to railroad end of train telemetry, andmore particularly to the reporting of end of train forces.

BACKGROUND

Within the railroad industry, end of train (EOT) units (sometimes alsoreferred to as end of train devices) are typically attached at the rearof the last car on a train, often to the unused coupling on the end ofthe last car opposite the head of the train. These EOT devices wereoriginally designed to perform some of the functions previouslyperformed by train personnel located in the caboose, thereby allowingtrains to operate without a caboose and with a reduced number of humanoperators.

Modern EOT units can perform a number of functions, some required by FRA(Federal Railroad Administration) regulations and some not. EOT unitsmonitor air pressure in the air brake pipe and transmit this informationto a head of the train (HOT) device located near the front of the train.EOT units also often include an end-of-train marker light to alerttrailing trains on the same track of the presence of the end of thetrain. Two-way EOT units (now required by FRA regulation in the U.S.)can accept a command from the HOT to open a valve to release pressure inthe air brake pipe so that the train's air brakes activate to stop thetrain in an emergency situation. Some EOT units include GPS receiversthat are used to transmit location information pertaining to the end ofthe train to HOT equipment as discussed in U.S. Pat. No. 6,081,769. EOTunits typically communicate with the HOT using radio-basedcommunications. This is because there is no hard-wired electricalconnection between the head of the train and the end of the train onsome trains, especially freight trains.

Some EOT units include motion detectors that are used to inform the HOTas to whether, and in some cases in which direction, a train is moving.In some EOT units, an accelerometer is used as the motion detector.Motion detection is reported by only a single bit (i.e., the single bitindicates only motion or lack thereof without any indication of speed ordirection) under AAR Standard S-5701 for “End-of-Train Communications.”The indication of train movement or lack thereof from the motiondetector, together with an indication of the head of train movement, maybe used by train personnel and/or computerized on-board train controlsystems to determine whether or not a train separation has occurred.However, such a determination is not very reliable given the single bitused to report motion pursuant to AAR Standard S-5701 because movementin opposite directions, and movement at significantly different speedsin the same direction, cannot be determined.

A somewhat more capable device is described in U.S. Pat. No. 6,087,950,which describes a motion detector that can be attached to an end oftrain unit. The motion detector includes a single axis accelerometer.The motion detector is configured to report a motion state that can bemoving or non-moving and a motion direction that can be forward orreverse.

More recently, EOT units that can communicate their positions to deviceslocated off of the train, such as those described in U.S. Pat. No.7,096,096 and in U.S. Pat. Pub. No. 2007/0170314 (the entire contents ofboth hereby being incorporated by reference herein), have become knownin the art. These communications allow personnel responsible for suchEOT units to locate them. Such communications can occur both when theEOT units are mounted on a train and when they are not mounted on anytrain.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantfeatures and advantages thereof will be readily obtained as the samebecome better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a system for reporting excessive EOT force according to oneembodiment of the invention.

FIGS. 2 a and 2 b are perspective and front views, respectively, of anEOT unit according to one embodiment of the invention.

FIG. 3 is a block diagram of the EOT unit of FIGS. 2 a and 2 b.

FIG. 4 is a flow chart illustrating a location reporting subroutineperformed by the end of train unit of FIG. 3.

FIG. 5 is a front view of a head of train device according to oneembodiment of the invention.

FIG. 6 is a block diagram of the head of train device of FIG. 5.

FIG. 7 is a flow chart illustrating processing performed by the head oftrain device of FIG. 5.

DETAILED DESCRIPTION

The present invention will be discussed with reference to preferredembodiments of end of train units. Specific details, such as messageformats and various reporting methods, are set forth in order to providea thorough understanding of the present invention. The preferredembodiments discussed herein should not be understood to limit theinvention. Furthermore, for ease of understanding, certain method stepsare delineated as separate steps; however, these steps should not beconstrued as necessarily distinct nor order dependent in theirperformance.

Excessive forces exerted on trains can damage both equipment (train andtrack) and cargo being carried on the train. Excessive forces applied toa train tends to become magnified at the end of the train. Suchexcessive forces can result from various causes. An operator can causeexcessive forces at the end of the train by accelerating too rapidly,which will cause a car at the end of the train to jerk in the directionof track once the slack between cars is taken up as the locomotive(s) atthe head of the train accelerate. An inexperienced operator, or even anexperienced operator who is operating a very long train, may not realizethe forces being exerted on an end of the train due to his/her actions.Another potential cause of excessive forces at the end of the train canresult from excessively “wavy” tracks that cause cars to sway rapidlyfrom side to side as the cars travel along the tracks. These forcesoccur mainly along an axis perpendicular to the track. Still anotherpotential cause of excessive forces at an end of a train are poor trackjoints, which may occur at grade crossings, bridges, or the like butwhich may also occur anywhere along a track. These forces tend to occurprimarily along an axis that is vertically oriented with respect to thetrack. Excessive forces at the end of the train can also be caused inother ways.

Because of the different possible causes for excessive forces at the endof the train, different actions are performed in different embodimentsdiscussed herein. The first step is to detect the occurrence of anexcessive force. This step may be performed using an accelerometerlocated in an end of train unit (it being understood that anaccelerometer measures acceleration, which is proportional to force). Inpreferred embodiments, the accelerometer is a tri-axial accelerometerwith the axes oriented such that a first axis is along a direction ofthe track, a second axis is along a direction perpendicular to the trackand a third axis is along a direction vertical to the track. Thisarrangement is advantageous in that it provides the ability to determinea direction along with an acceleration has occurred, which may beindicative of the cause of the acceleration (e.g., a sudden verticalacceleration may result from a problem with the track whereas a suddenacceleration in a direction of a track may result from an operatoraccelerating a train from a stopped position too rapidly). In otherembodiments, a single or dual axis accelerometer is used. Suchembodiments may employ one or more accelerometers along one of the threeaxes discussed above, or may orient the accelerometer such that it issensitive to accelerations in more than one axis as discussed in U.S.Pat. No. 6,087,950. Embodiments utilizing a single accelerometer can beless expensive than embodiments employing multiple accelerometers ormultiple axis accelerometers.

The accelerometer(s) may be periodically polled in real time to detectforces greater than a threshold. Alternatively, a triggering circuitsuch as a one-shot may be used to generate an interrupt when theaccelerometer measures a force greater than the threshold. Theaccelerations reported by the accelerometers are typically“instantaneous” accelerations, and these instantaneous accelerations areused directly in some embodiments. In other embodiments, a plurality ofinstantaneous accelerations are filtered (e.g., moving window averagefiltering, Kalman filtering, etc.).

Various embodiments employ different thresholds. In some embodiments,the threshold may be fixed. In such embodiments, the threshold may beset to an acceleration based on a safety factor and maximum force forwhich a typical car coupling can withstand divided by a maximum carweight. A typical freight car coupling in use in the U.S. can withstanda force of about 350,000 pounds, and a current maximum expected carweight in the U.S. freight railroad industry is 268,000 pounds (thisrepresents the weight of the car plus a maximum cargo). In someembodiments, the acceleration threshold based on these values and asafety factor is chosen as 1 g. The threshold is preferably 0.25 g orgreater to ensure that accelerations associated with normal movement ofthe train are not reported as excessive. In yet other embodiments, thethreshold is set dynamically. The threshold may be set dynamically basedon a particular cargo being carried on the train, particular equipment(e.g., couplings, types of cars) used on the train, or any other factorwhich may affect a desirable maximum EOT force.

Once an excessive force has been detected, the detection must becommunicated. The communication may occur immediately or soon after thedetection has been made, and/or the detection may be recorded andcommunicated later. In some embodiments, the occurrence of the excessiveforce is communicated to a head of train device for display to anoperator immediately or soon after the detection occurs (such displaybeing different from the manner in which an indication of movement ofthe train is normally displayed to the operator). The message and/ordisplay may include a simple indication that an acceleration greaterthan the threshold has been observed, or may include the actual(preferably instantaneous) acceleration (or accelerations in multipleaxis accelerometer embodiments) measured by the accelerometer. In suchembodiments, the head of train device relays the message to a centraloffice, either in addition to or instead of displaying the message. Inother embodiments, the EOT device may transmit the message directly to acentral data collection site. For example, EOTs equipped for long rangecommunication with a central site (e.g., via a cellular modem thatcommunicates with a cellular base station) are disclosed in U.S. Pat.Pub. No. 2007/0170314. As disclosed in that publication, the EOT mayperiodically transmit a message including the EOT location.

In some embodiments, the message further includes information (e.g., anamount of excessive force or an indication that an excessive force hasbeen detected together with a location and/or time at which theexcessive force was detected). In yet other embodiments, the EOT deviceincludes an event recorder which records information pertaining to theexcessive force. The data from the EOT device is accessed later andappropriate action (e.g., informing the operator of the excessive forceif the operator was the cause, repairing the section of track causingthe excessive force) is taken. In still other embodiments, an excessiveforce detection message sent from the EOT to the HOT is recorded in anevent recorder included in the HOT device and/or forwarded from the HOTdevice to the train's main event recorder. Still other methods forcommunicating the detection of an excessive force are possible.

An exemplary embodiment of an EOT force reporting system will now bediscussed. This embodiment will include multiple EOT force reportingmethods as discussed above. It should be understood that otherembodiments employ less than all of, or alternatives to, the reportingmethods discussed in connection with this embodiment.

FIG. 1 is a block diagram of a system 10 for measuring and reporting EOTforces. The system includes an EOT unit 100 configured for wirelesscommunications with an HOT device 300. The HOT device 300 is connectedto an event recorder 301. The EOT unit 100, the HOT device 300 and theevent recorder 301 are all located onboard a train. The HOT device 300is configured for wireless communications with a central office 303. TheEOT unit 100 is also configured for wireless communications with and EOTTracking Facility 302.

FIGS. 2 a and 2 b illustrate an embodiment of the EOT unit 100. The EOTunit 100 includes a housing 110 in which the internal components of theEOT unit 100 (discussed in further detail below) are located. A handle111 is attached to the housing 110 to facilitate the installation andremoval of the EOT unit 100 from a train car. Also attached to thehousing is a connector 120 for connecting the EOT unit 100 to an airbrake hose 10 which is in fluid communication with the train's air brakepipe (not shown in FIG. 2 a or 2 b). Also attached to the housing 110 isa coupler 130 which couples the EOT unit 100 to a train car coupling.The EOT unit 100 also includes a marker light 140 attached to thehousing 110. Three antennas are also attached to the housing 110: afirst antenna 150 for communicating with the HOT, a second antenna 160for communicating with a cellular base station network, and a thirdantenna 170 for receiving messages from GPS satellites.

A block diagram 30 of the EOT unit 100 of FIG. 1 is illustrated in FIG.3. The EOT unit 100 is controlled by a processor 210. The processor 210receives power from a power subsystem 220 which includes an air-poweredelectrical generator 221 connected to the air brake pipe 10, a rectifier222, a voltage regulator 223 and one or more batteries 224. Detailsconcerning the power subsystem 220 are discussed in greater detail incorresponding U.S. Pat. No. 7,096,096.

The processor 210 is connected to control an EOT marker light 140(although a direct connection is illustrated in FIG. 2, those of skillin the art will understand that the processor 210 may supply the controlof power to the EOT marker light 140 via a relay or similar device) inaccordance with applicable FRA regulations. Also connected to theprocessor 210 is a tilt sensor 230. The processor 210 uses the tiltsensor 230, among other things, to determine when the EOT unit 100 hasbeen placed in a horizontal position so that the processor 210 can takethe EOT unit to a low power state to conserve battery power.

Also connected to the processor 210 is an air pressure transducer 240,which is in fluid communication with the air brake pipe 10 and isconfigured to detect the pressure in the air brake pipe 10. Theprocessor 210 reads the pressure in the air brake pipe 10 reported bythe transducer 240 and periodically transmits this and other informationto the HOT using the HOT transceiver 250. Under AAR Standard S-5701, thereport occurs once every 55-65 seconds in the absence of significantpressure changes. The format of an exemplary report is set forth below:

TABLE 1 FRA Message Guidelines - Standard S-5701 Basic Bit sync 69 bitsBlock Frame sync 11 bits Chaining bits 2 bits Device battery condition 2bits Message type identifier 3 bits Unit address code 17 bits Rear brakepipe status and pressure 7 bits Discretionary information 11 bits*Motion detection 1 bit Marker light battery condition 1 bit Marker lightstatus 1 bit Basic block BCH code 18 bits Trailing bit 1 bit TotalLength 144 bits Optional Bit sync 69 bits Block(s) Frame sync 11 bitsChaining bits 2 bits Block format indicator bit 1 bit Optional blockdata bits 42 bits Optional block BCH code 18 bits Trailing bit 1 bitTotal length 144 bits *For two-way systems, see paragraph 3.0.In embodiments in which excessive EOT forces are reported to the HOTdevice 300, the occurrence and/or measurement(s) (e.g., magnitudes) ofexcessive accelerations can be included in the “optional block databits” portion of the message described above or may be sent in aseparate message.

An emergency solenoid 280 is also connected to the processor 210 and theair brake pipe 10. When the processor 210 receives an emergency brakingcommand from the HOT via the HOT transceiver 250, the processor 210controls the solenoid 280 to open, causing a loss of pressure in the airbrake pipe 10 and activation of the train's brakes. In some embodiments,another solenoid (not shown in FIG. 2) is also connected to theprocessor 210 and between the air brake pipe 10 and the air poweredgenerator 221. This solenoid is used to perform certain tests requiredby the FRA.

An accelerometer 290 is also connected to the processor 210. Asdiscussed above, the accelerometer may be a single axis, dual axis orthree axis accelerometer in various embodiments. Those of skill in theart will recognize that the signals from some accelerometers may be inanalog form and that an analog-to-digital (A/D) converter (not shown inFIG. 3) may be used to convert the analog sensor signal to digital formif the processor 210 does not include an integral A/D converter. Theaccelerometer 290 preferably measures instantaneous acceleration. Theprocessor 210 is configured to filter the instantaneous accelerationreported from the accelerometer in some embodiments; in otherembodiments, no filtering is used. In embodiments in which filtering ofthe instantaneous accelerations measured by the accelerometer isemployed, care must be taken in choosing the filtering parameters suchthat sensitivity to accelerations of short temporal duration (such asthose that may occur when an end of train is first forced into motionfrom a stopped state by a locomotive) are not missed. Some embodimentsemploy a moving window average filter with a window size of the threemost recent readings, with readings being taken every 10 milliseconds.

Also connected to the processor 210 is an event recorder 295. The eventrecorder 295 records data pertinent to the EOT unit 100, such as thecontent and time of transmission of various messages sent and receivedby the EOT unit 100. As discussed above, the occurrence of excessiveacceleration events are also recorded for later retrieval in someembodiments. The data recorded for such events can include the date,time, and location of the train at the time of the event as reported bythe positioning system 270 plus other circumstances surrounding theevent.

The processor 210 is further connected to a positioning system 270,which is a GPS receiver in preferred embodiments but may also be an INS(intertial navigation system), LORAN device, or any other positioningsystem. The positioning system 270 supplies the processor 210 withreports on the position of the EOT unit 100.

The processor 210 is also connected to a cellular modem 260. Theprocessor 210 uses the cellular modem to send reports including anidentifier of the EOT unit 100 and location (and preferably time)information obtained from the positioning system 270 to an EOT trackingstation at periodic intervals. The processor 210 also receives “page”messages (messages requesting the EOT unit to report its currentlocation) and “disable” messages (messages instructing the EOT unit toenter an non-operational state) via the cellular modem 260. In additionto reporting EOT location to the EOT tracking facility 302, the cellularmodem 260 may also report excessive accelerations detected by theaccelerometer 290. This reporting is in addition to (or, in someembodiments, in lieu of, the reporting accomplished via recording at theEOT event recorder 295, the display at the HOT device 300, and/or therecording at the event recorder 301).

During normal operation, the processor 210 controls the EOT marker light140, communicates air brake pipe pressure information to the HOT,activates the emergency solenoid 280 in response to commands from theHOT, communicates train position to the EOT tracking facility 302 andperforms other functions that will not be discussed further herein toavoid obscuring this disclosure.

In addition to the operations discussed above, the processor 210monitors the accelerometer 290 in order to detect excessiveaccelerations. A flowchart 400 of the operations performed by theprocessor 210 is shown in FIG. 4. The processor reads the accelerometer290 at step 402 and uses the value read (which is an instantaneousacceleration in this embodiment) to calculate a filtered accelerationvalue at step 404. In some embodiments, the filtering algorithm is amoving window filter with a width of three accelerations values. Theprocessor 210 then compares the filtered acceleration to a threshold atstep 406. The threshold may be a fixed value, or may be set by anoperator of the train on which the EOT unit 100 is mounted andcommunicated by messages received from the HOT device, or may becommunicated to the EOT unit 100 via a message received on the cellularmodem 260 from the EOT Tracking Facility 302. Others ways of setting thethreshold are also possible. The comparison of step 210 may be anabsolute value comparison (i.e., the absolute value of the accelerationis compared to a threshold) or may be a signed value comparison. Anabsolute value comparison is preferable in some circumstances (e.g., inconnection with an accelerometer measuring vertical acceleration for thepurpose of detecting track defects) whereas a signed value comparison ispreferable in others (e.g., in connection with an accelerometermeasuring acceleration in the direction of the track for the purpose ofdetecting accelerations caused by an operator incorrectly startingmovement of a train).

If the filtered acceleration is below the threshold, no reporting isnecessary and the processor 210 delays a period of time (100 ms in someembodiments) at step 408 before repeating step 402. If the filteredacceleration exceeds the threshold at step 406, the processor 210records the filtered acceleration in the EOT event recorder 295 at step410. Next, the processor 210 reports the filtered acceleration to theEOT Tracking Facility 302 via the cellular modem 260 at step 412. Theprocessor 210 then reports the filtered acceleration to the HOT device300 at step 414. The processor then delays for a brief period at step408 before repeating steps 402 and following.

The HOT device 300 of FIG. 1 is shown in more detail in FIG. 5. Asdiscussed above, the HOT device is typically (but not necessarily)mounted in a locomotive at the head of the train. In North America, theHOT device 300 communicates with the EOT unit 100 using a short range2-watt digital radio transceiver over certain frequencies assigned bythe FCC in the U.S. Additional details concerning HOT device/EOT unitcommunications can be found in U.S. patent application Ser. No.11/929,605, the contents of which are hereby incorporated by referenceherein. Shown in FIG. 5 is an EOT emergency switch 342 for use by anoperator in initiating an emergency braking operation. A display 350indicates the brake pressure measured by the EOT unit 100, and a seconddisplay 351 is used for displaying various messages including a messageindicating that an excessive EOT force/acceleration has been detectedcan be displayed to the operator. A keypad 340 is available to theoperator for entering data such as the serial number of the EOT unit 100with which the HOT device 300 is to communicate. Various indicators 330,some of which are combined with push buttons are available for use bythe operator as described further in the above-mentioned application.One of the indicators 330 indicates to the operator when the train is inmotion.

A block diagram of the HOT device 300 is shown in FIG. 6. The HOT deviceincludes a processor 320 which is connected to a memory (the memory isshown onboard the processor 320 in FIG. 6, but those of skill in the artwill recognize that one or more external memories, such as ROM, RAM,etc. may also be used). The processor 320 is connected (via an interfacenot shown in FIG. 6) to a train event recorder 301. An EOT transceiver330 is also connected to the processor 320 for communications with anEOT unit 100. A speed sensor input port 360 connects the processor 320to a speed sensor 470. A GPS receiver 480 is also connected to theprocessor 320 in some embodiments (this is particularly useful in theevent that the EOT unit 100 does not include its own GPS receiver; inthis case, the GPS position from the GPS receiver 480 can be used todetermine and report the location of the train upon the receipt of anexcessive EOT force message from the EOT unit 100 and an approximate EOTlocation can be calculated with knowledge of a length of the train).

FIG. 7 is a flowchart 600 illustrating operations performed by the HOTdevice 300 in some embodiments of the invention. Less than all of thereporting steps illustrated in FIG. 6 may be performed in variousalternative embodiments. The flowchart of FIG. 7 is suitable forimplementation as a subroutine called upon receipt of a message from theEOT unit 100. The EOT message is read at step 402. The processor 320determines the type of message at step 404. If the EOT message is amessage other than an excessive force message, other processing (whichshall not be discussed in detail herein to avoid obscuring theinvention) is performed at step 406.

If the message from the EOT does indicate that an excessive EOT forcehas been detected by the EOT unit 100 at step 404, a message isdisplayed at the HOT display 351 at step 408. In those embodiments inwhich the excessive force message from the EOT only indicates that anexcessive EOT force has been detected, the message in the display 351may simply indicate “EXCS EOT ACC DET.” In those embodiments in whichthe detected EOT force is reported in the message from the EOT, the HOTmay display a message such as “EOT ACC XXG DET,” where XX represents theEOT acceleration (filtered or unfiltered) reported by the EOT unit 100.In those embodiments utilizing a triaxial accelerometer, the messageshown to the operator in display 351 may also include an X, Y, or Z toindicate the axis on which the excessive EOT acceleration occurred. Insome embodiments, the processor 320 may take corrective action, such asrequiring the operator to acknowledge the excessive acceleration (e.g.,by pushing one of the indicator buttons 330 or keys 340) or forcing anemergency braking operation in the event that no acknowledgement fromthe operator is received. Such corrective action may occur only when theEOT acceleration exceeds a second, higher threshold and/or only after acertain number of excessive accelerations have been detected in someperiod of time in some embodiments. In yet other embodiments, theprocessor 320 requires an operator acknowledgement if a first thresholdis exceeded and initiates an emergency braking operation if the secondthreshold is exceeded.

It should be noted that, in some embodiments, the accelerometer may beused to both a) determine whether the train is in motion, and b) detectexcessive EOT acceleration. In such embodiments, a first threshold isused for the former and a second, higher threshold is used for thelatter. Such embodiment may also employ a still higher third thresholdthat can be used to include an indication in a message to a head oftrain device that the train's brakes should be activated (alternatively,the third threshold can be implemented in the HOT device).

Next, the processor 320 records the occurrence of the excessive EOTforce at the event recorder 301 at step 410 and transmits a message to acentral office (e.g., a dispatcher) at step 412. The next EOT message isthen processed at step 402. Alternatively, in embodiments in which theexcessive force indication is in a message with the format of Table 1,the rest of the message is processed at step 406.

Those of skill in the art will recognize that various modifications tothe EOT unit 100 are possible. For example, it is possible to operatethe EOT unit 100 solely with battery power rather than using batteriesin conjunction with an air powered generator. Cellular modem 260 may bereplaced with any type of wireless communication system. Various othermodifications to the components of the EOT unit 100 are also possible.

Furthermore, the purpose of the Abstract is to enable the U.S. Patentand Trademark Office and the public generally, and especially thescientists, engineers and practitioners in the art who are not familiarwith patent or legal terms or phraseology, to determine quickly from acursory inspection the nature and essence of the technical disclosure ofthe application. The Abstract is not intended to be limiting as to thescope of the present invention in any way.

While the invention has been described with respect to certain specificembodiments, it will be appreciated that many modifications and changesmay be made by those skilled in the art without departing from thespirit of the invention. It is intended therefore, by the appendedclaims to cover all such modifications and changes as fall within thetrue spirit and scope of the invention.

1. An end of train unit suitable for use on a train, the end of trainunit comprising: a processor connected to a housing; a first couplingconnected to the housing, the first coupling being configured to engagea train coupling; an end of train marker light connected to the housingand configured to be controlled by the processor; a pressure transducerconnected to the processor and in fluid communication with a secondcoupling connectable to an air brake pipe of a train; an accelerometerconnected to the processor; and a first transmitter connected to theprocessor; wherein the processor is configured to perform the steps ofreceiving an acceleration from the accelerometer; performing acomparison of the acceleration to a threshold; determining that theacceleration exceeds the threshold; and transmitting a message via thefirst transmitter in response to the acceleration exceeding thethreshold.
 2. The end of train unit of claim 1, wherein the messageincludes an identifier of the end of train unit and wherein the firsttransmitter is a wireless transmitter configured to transmit the messagewirelessly to a head of train device.
 3. The end of train unit of claim1, wherein the message includes an identifier of the end of train unitand an address of a device located off of the train, and the firsttransmitter is a wireless transmitter configured to transmit the messagewirelessly.
 4. The end of train unit of claim 1, further comprising: anevent recorder connected to the processor; wherein the first transmittertransmits the message to the event recorder.
 5. The end of train unit ofclaim 1, wherein the message includes a time corresponding to theacceleration.
 6. The end of train unit of claim 1 further comprising: apositioning system connected to the processor; wherein the messageincludes a position corresponding to the acceleration.
 7. The end oftrain unit of claim 1, wherein the threshold is at least 0.25 g.
 8. Theend of train unit of claim 1, wherein the message includes a magnitudeof the acceleration.
 9. The end of train unit of claim 1, wherein themessage includes an indication that an acceleration in excess of thethreshold has been detected.
 10. The end of train unit of claim 1,wherein the acceleration is an instantaneous acceleration.
 11. The endof train unit of claim 1, wherein the acceleration is a filteredacceleration.
 12. The end of train unit of claim 1, wherein thecomparison is an absolute value comparison.
 13. The end of train unit ofclaim 1, wherein the accelerometer is a triaxial accelerometer.
 14. Theend of train unit of claim 13, wherein the message indicates anorientation of the acceleration.
 15. The end of train unit of claim 1,wherein the message includes a magnitude for acceleration in each axisof the triaxial accelerometer.
 16. An end of train unit comprising: aprocessor connected to a housing; a first coupling connected to thehousing, the first coupling being configured to engage a train coupling;an end of train marker light connected to the housing and configured tobe controlled by the processor; a pressure transducer connected to theprocessor and in fluid communication with a second coupling connectableto an air brake pipe of a train; an accelerometer connected to theprocessor; and a first transmitter connected to the processor; whereinthe processor is configured to perform the steps of receiving anacceleration from the accelerometer; performing a comparison of theacceleration to a threshold; determining that the acceleration exceedsthe threshold; and transmitting a message including a magnitude of theacceleration via the first transmitter.
 17. A head of train devicecomprising: a processor; a wireless receiver connected to the processor;and a display connected to the processor; wherein the processor isconfigured to perform the steps of receiving a message from an end oftrain unit, the message indicating that an excessive end of trainacceleration has been detected; and reporting the excessive end of trainforce.
 18. The head of train device of claim 17, wherein the processoris configured to display an indication that the excessive end of trainforce acceleration has been detected on the display.
 19. The head oftrain device of claim 17, further comprising: an interface to an eventrecorder, the interface being connected to the processor; wherein theprocessor is further configured to record the message on the eventrecorder.
 20. The head of train device of claim 19, wherein theprocessor is further configured to perform the step of: taking acorrective action if an acknowledgment of the display of the excessiveend of train acceleration is not received from an operator.
 21. The headof train device of claim 20, wherein the corrective action comprisesactivating the train's brakes.
 22. The head of train device of claim 17,wherein the processor is further configured to perform the step of:comparing the acceleration to a higher threshold; and taking correctiveaction if the acceleration exceeds the higher threshold.
 23. The end oftrain device of claim 22, wherein the corrective action comprisesactivating the train's brakes.